1. Field of the Invention
The present invention relates to an image reading apparatus and more specifically to an image reading apparatus for optically reading an image recorded on an original which is to be read such as a photographic film.
2. Description of the Related Art
According to photographic processing methods proposed recently, a film image recorded on a photographic film is separated into components of red, green and blue and is read. The image data obtained from the reading is subjected to various types of corrections and recorded on a recording material or displayed on a display unit. Note that the term photographic film used here refers to a film whose negative image or positive image is visualized by development after a photograph has been taken of an object.
Technology for realizing an image reading apparatus for use in reading the film image in this type of photographic processing method has been proposed in, for example, Japanese Patent Application Laid-Open No. 6-233052, in which is disclosed a plurality of photoelectric conversion elements having different photometric amount limits (saturation light amount) are used as image sensors and depending on the amount of light carrying image information, the photoelectric conversion devices are selected, there by making it possible to read an image over a wide dynamic range.
However, because the technology described in the aforementioned JP-A No. 6-233052 is not provided with means for adjusting the width of the luminous flux passing through image-forming lens for forming an image on a photoelectric conversion element, it is not capable of reading an image with an optimum luminous flux width corresponding to the reading determining conditions (the conditions for determining the reading conditions) and it is not possible to always obtain high quality image data from all types of reading determining conditions.
Namely, although if a high resolution reading is required, the focusing magnification of the focusing lens needs to be increased to obtain image data composed of many pixels, in this case, the depth of field becomes shallow so that the picture quality deteriorates. Although the width of luminous flux passing the focusing lens is required to be smaller to respond to this phenomenon, because the technology described in the above JP-A No. 6-233052 has no means for adjusting this luminous flux width, high quality image data cannot be obtained.
Accordingly, the present invention has been achieved to solve the above problems, and therefore, it is an object of the invention to provide an image reading apparatus capable of obtaining high quality image data in accordance with reading determining conditions.
To achieve the above object, according to a first aspect of the present invention, there is provided an image reading apparatus comprising: a light source for illuminating an original object to be read; focusing means provided with a diaphragm capable of altering the width of the luminous flux of a light beam projected through the diaphragm, and for focusing an image recorded on said original document to be read; an image sensor for separating said image recorded on said original document to be read, reading said image, and outputting said image as image data when a light which has passed through said focusing means is projected onto said image sensor; and control means for controlling the state of said diaphragm for adjusting the width of said luminous flux in accordance with the reading determining conditions of the original object to be read.
In the image reading apparatus of the first aspect of the invention, an original object to be read is illuminated by a light source and an image recorded on the original object to be read is focused by a focusing means having a diaphragm capable of changing the luminous flux width of a projected beam. Then, an image recorded on the original object to be read is separated into a plurality of pixels and read, so that it is output in the form of image data. The above original object to be read includes transparent originals and reflective originals. The above image sensor includes a line CCD and area CCD.
In the image reading apparatus of the first aspect of the present invention, the state of the diaphragm provided on the focusing means is controlled by the control means so as to adjust the luminous flux width of light projected into the focusing means in accordance with the reading determining conditions of the original object to be read.
As described above, in the image reading apparatus of the first aspect of the present invention, the focusing means contains a diaphragm capable of changing the luminous flux width of the projected light and the condition of the diaphragm is controlled so that the luminous flux width is adjusted in accordance with the reading determining conditions of the original object to be read. Therefore, the luminous flux width of light passing through the focusing means can be controlled to the optimum width in accordance with the reading determining conditions, so that high quality image data can be obtained.
According to a second aspect of the present invention, there is provided an image reading apparatus according to claim 1, wherein one of said reading determining conditions is a focusing magnification of said focusing means and said control means controls the state of said diaphragm so that the higher said focusing magnification, the smaller the width of said luminous flux.
In the image reading apparatus of the second aspect of the present invention, one of the reading determining conditions according to the first aspect is a focusing magnification of the focusing means and the condition of the diaphragm is controlled by the control means so that the higher the focusing magnification, the smaller the luminous flux width.
That is, generally the higher the focusing magnification of the focusing means, the shallower the depth of field, so that the picture quality deteriorates. To suppress the deterioration of the picture quality, the luminous flux width of light passing through the focusing means is controlled so as to become smaller as the focusing magnification increases.
As described above, in the image reading apparatus of the second aspect of the present invention, one of the reading determining conditions according to the first aspect is a focusing magnification and further, the condition of the diaphragm is controlled so that the higher the focusing magnification, the smaller the luminous flux width. Therefore, the optimum luminous flux width can be set in accordance with the focusing magnification so that high quality image data can be obtained.
According to a third aspect of the present invention, there is provided an image reading apparatus according to claim 1, wherein one of said reading determining conditions is the effective F number on said original object to be read and said control means controls the state of said diaphragm so that said effective F number is constant.
In the image reading apparatus of the third aspect of the present invention, one of the reading determining conditions according to the first aspect is the effective F number of the original object to be read and the condition of the diaphragm is controlled by the control means so that the effective F number is constant.
The effective F number of the original object to be read is proportional to the F number indicating the brightness of the optical system (the brighter, the smaller) and proportional to an inverse number of the focusing magnification. Therefore, to make such a effective F number constant, the F number is increased as the focusing magnification is increased. To increase the F number, the optical system needs to be darkened. Therefore, to make the effective F number constant, the diaphragm is controlled so that the luminous flux width of light passing through the focusing means is reduced as the focusing magnification is increased.
As described above, in the image reading apparatus of the third aspect of the present invention, one of the reading determining conditions according to the first aspect is the effective F number of the original object to be read and the condition of the diaphragm is controlled so that the effective F number is constant. Therefore, the optimum luminous flux width in accordance with the focusing magnification of the focusing means can be set so that high quality image data can be obtained.
According to a fourth aspect of the present invention, there is provided an image reading apparatus according to claim 1, wherein one of said reading determining conditions is the density of said original object to be read and said control means controls the state of said diaphragm so that the higher said density, the larger the width of said luminous flux.
In the image reading apparatus of the fourth aspect of the present invention, one of the reading determining conditions according to the first aspect is the density of the original object to be read and the condition of the diaphragm is controlled so that the higher the density, the larger the luminous flux width.
Namely, because the amount of light passing through the original object to be read or reflected from the original object to be read is decreased as the density of the original object to be read is increased, in this case, by increasing the luminous flux width of light passing through the focusing means, a reduction of light amount due to the density of the original object to be read is compensated.
As described, in the image reading apparatus of the fourth aspect of the present invention, because one of the reading determining conditions according to the first aspect is the density of the original object to be read and the condition of the diaphragm is controlled so that the higher the density, the larger the luminous flux width, the optimum luminous flux width in accordance with the density of the original object to be read can be set so that high quality image data can be obtained.
According to the image reading apparatus of a fifth aspect of the present invention, there is provided an image reading apparatus according to claim 1, wherein one of said reading determining conditions is the reading speed for said original object to be read and said control means controls the state of said diaphragm so that the faster said reading speed, the larger the width of said luminous flux.
In the image reading apparatus of the fifth aspect of the present invention, one of the reading determining conditions according to the first aspect is the reading speed for the original object to be read and the condition of the diaphragm is controlled so that the faster the reading speed, the larger the luminous flux width.
Namely, because the faster the reading speed for the original object to be read becomes, the shorter the reading time by the image sensor becomes, and in the case where the image sensor is, for example, a CCD sensor, the electric charge accumulation time per unit time is shortened, by enlarging the luminous flux width of light passing through the focusing means, a drop in the reading sensitivity of the image sensor accompanied by a reduction of the electric charge accumulating time caused by the increased reading speed for the original object to be read is compensated.
As described above, in the image reading apparatus of the fifth aspect of the present invention, because one of the reading determining conditions according to the first aspect is reading speed for the original object to be read and the diaphragm is controlled so that the faster the reading speed, the larger the luminous flux width, an optimum luminous flux width in accordance with the reading speed for the original object to be read can be set, so that high quality image data can be obtained.
According to a sixth aspect of the present invention, there is provided an image reading apparatus according to claim 1, wherein one of said reading determining conditions is the amount of unevenness on the surface of said original object to be read and said control means controls the state of said diaphragm so that the larger the amount of said unevenness, the smaller the width of said luminous flux.
In the image reading apparatus of the sixth aspect of the present invention, one of the reading determining conditions according to the first aspect is the amount of unevenness of the surface of the original object to be read and the condition of the diaphragm is controlled by the control means so that the larger the amount of unevenness, the smaller the luminous flux width.
That is, because the larger the amount of unevenness of the surface of the original object to be read becomes, the more the picture quality deteriorates, by reducing the luminous flux width of light passing through the focusing means, the deterioration of the picture quality due to the amount of unevenness of the surface of the original object to be read is suppressed.
As described above, in the image reading apparatus of the sixth aspect of the present invention, because one of the reading determining conditions according to the first aspect is the amount of unevenness of the surface of the original object to be read and the condition of the diaphragm is controlled so that the larger the amount of unevenness becomes, the smaller the luminous flux width becomes, an optimum luminous flux width in accordance with the amount of unevenness of the original object to be read can be set, so that high quality image data can be obtained.
According to a seventh aspect of the present invention, there is provided an image reading apparatus according to claim 1, wherein one of said reading determining conditions is the degree of diffusion of said original object to be read and said control means controls the state of said diaphragm so that the larger said degree of diffusion, the larger the width of said luminous flux.
In the image reading apparatus of the seventh aspect of the present invention, one of the reading determining conditions according to the first aspect is the degree of diffusion of the original object to be read and the condition of the diaphragm is controlled by the control means so that the larger the degree of diffusion, the larger the luminous flux width.
Namely, when the original object to be read is a monochrome film, the ratio of silver existing therein is higher as compared to color film so that the degree of diffusion of the light passing through the focusing means is high and the degree of reduction of the light amount is high. Therefore, by increasing the luminous flux width of light passing through the focusing means, the reduction of the light amount caused by the degree of diffusion of the original object to be read is compensated.
As described above, in the image reading apparatus of the seventh aspect of the present invention, because one of the reading determining conditions according to the first aspect is the degree of diffusion of the original object to be read and the condition of the diaphragm is controlled so that the larger the degree of diffusion becomes, the larger the luminous flux width becomes, the optimum luminous flux width corresponding to the degree of diffusion of the original object to be read can be set, so that high quality image data can be obtained.
According to an eighth aspect of the present invention, there is provided an image reading apparatus according to claim 1, wherein one of said reading determining conditions is the reading size of said original object to be read and said control means control the state of said diaphragm so that the larger said reading size, the smaller the width of said luminous flux.
In the image reading apparatus of the eighth aspect of the present invention, one of the reading determining_conditions according to the first aspect is the reading size of the original object to be read and the condition of the diaphragm is controlled by the control means so that the larger the reading size, the smaller the luminous flux width.
Namely, because the larger the reading size for the original object to be read becomes, the more the focusing means is affected by the vignetting, by reducing the luminous flux width of light passing through the focusing means, the influence of the vignetting caused by the extent of the reading size of the above original object to be read is suppressed.
As described above, in the image reading apparatus of the eighth aspect of the present invention, because one of the reading determining conditions according to the first aspect is the reading size of the original object to be read and the condition of the diaphragm is controlled so that the larger the reading width, the smaller the luminous flux width, the optimum luminous flux width in accordance with the reading size of the original object to be read can be set, so that high quality image data can be obtained.
It should be noted here that in order to increase the speed at which an image is read by an image reading apparatus, a preliminary reading of the image at comparatively high speed and low level of detail (referred to as a prescan in the present specification) is performed, and on the basis of the image data obtained from the prescan, the main reading of the image is performed at a comparatively low speed and at a high level of detail (referred to as a fine scan in the present specification) Each time a prescan and fine scan are performed, the reading conditions and the processing conditions for each type of image processing to be performed on the image data to be obtained from the fine scan are determined. The fine scan is performed under the determined reading conditions and image processing is performed in accordance with the above determined processing conditions on the image data obtained from the fine scan.
In this way, the speed at which the image is read in this type of image reading apparatus is faster during the prescan than during the fine scan.
According to the ninth aspect of the present invention, there is provided an image reading apparatus according to claim 1, wherein one of the reading determining conditions is the scanning state and the condition of the diaphragm is controlled so that the width of the luminous flux is greater for a prescan than for a fine scan.
In the image reading aspect of the ninth aspect of the invention, one of the reading determining conditions according to the first aspect is the scanning state and the condition of the diaphragm is controlled by the control means so that the width of the luminous flux is greater when the scanning state is a prescan scanning state than when the scanning state is a fine scan scanning state.
Namely, as is stated above, the speed at which the image is read during a prescan is faster than the speed at which the image is read during a fine scan. The faster the speed at which the image is read, however, the shorter the reading time by the image sensor, and when the image sensor is, for example, a CCD sensor, the shortening of the charge accumulation time per time unit is as described above.
Accordingly, by increasing the width of the luminous flux of light passing through focussing means, compensation can be made for the above time reduction in the charge accumulation time.
As described above, in the image reading apparatus of the ninth aspect of the invention, because one of the reading determining conditions according to the first aspect is the scanning state and the condition of the diaphragm is controlled so that the width of the luminous flux is greater when the scanning state is a prescan scanning state than when the scanning state is a fine scan scanning state, the optimum luminous flux width in accordance with the reading size of the original object to be read can be set, so that high quality image data can be obtained.
In the image reading apparatus of the tenth aspect of the present invention, one of the reading determining conditions according to the first aspect is the state in which the original object to be read is held, and the condition of the diaphragm is controlled by the control means so that when the original object to be read is held in a mounted state, the width of the luminous flux is reduced.
Namely, when the original object to be read is held in a mounted state, the greater the amount of variation in the width of the mounted member, the greater the deterioration in the image quality. Therefore, by reducing the width of the luminous flux of light passing through the focussing means, the depth of field can be increased which enables the deterioration in the image quality caused by variations in the thickness of the mounted member to be suppressed.
As described above, in the image reading apparatus of the tenth aspect of the present invention, because one of the reading determining conditions according to the first aspect is the state in which the original object to be read is held and the condition of the diaphragm is controlled so that the width of the luminous flux is reduced when the original object to be read is held in a mounted state, the optimum luminous flux width in accordance with the state in which the original object to be read is held can be set, so that high quality image data can be obtained.
According to an eleventh aspect of the present invention, there is provided an image reading apparatus according to claim 1, wherein reading determining conditions for reading said original object to be read include at least two of the focusing magnification, the effective F number, the density, the reading speed, the amount of unevenness, the degree of diffusion, the reading size, the scanning state, and the holding state of said original object to be read and said control means controls the state of said diaphragm according to said reading determining conditions.
In the image reading apparatus of the eleventh aspect of the present invention, the reading determining conditions according to the first aspect include at least two of the focusing magnification of the original object to be read, the effective F number of the original object to be read, the density, the reading speed, the amount of unevenness, the degree of diffusion, the reading size, the scanning state, and the holding state of the original object to be read_and the condition of the diaphragm is controlled by the control means based on the above mentioned reading determining conditions.
As described above, in the image reading apparatus of the eleventh aspect of the present invention, because the reading conditions according to the first aspect include at least two of the focusing magnification, effective F number, density, reading speed, amount of unevenness, amount of diffusion, reading size, scanning state, and holding state of the original object to be read and the condition of the diaphragm is controlled based on the reading determining conditions, the optimum luminous flux width in accordance with at least two of the above reading determining conditions can be set, so that high quality image data can be obtained.
According to a twelfth aspect of the present invention, there is provided an image reading apparatus according to the first aspect further comprising a light amount control means capable of controlling the amount of light for illuminating said original object to be read.
In the image reading apparatus of the twelfth aspect of the present invention, because the first aspect is provided with a light amount control means capable of controlling the amount of light irradiated over the original object to be read, the optimum light amount and luminous flux width corresponding to the reading determining conditions can be set, so that high quality image data can be obtained.